#include <stdio.h>
#include <math.h>

double distance(double x1, double y1,double x2, double y2) {
    double dx = x1 - x2;
    double dy = y1 - y2;
    double dis = sqrt(dx * dx + dy * dy);
    return dis;
}

int main() {
    double x1 = 0, y1 = 0, x2 = 1, y2 = 1;
    double dis = distance(x1, y1, x2, y2);
    printf("%f", dis);
    return 0;
}